Method and apparatus for determining liquid level



June 12, 1945. D. G. c. HARE 2,378,219

METHOD AND APPARATUS FOR DETERMINING LIQUID LEVEL Original Filed May 29, 1940 4a 42 i 40 46 g f 35 #1 k I 34 1 i I} el 513 1. 2

50 A WM INVENTOR Patented June 12, 1945 $378,219: I

METHOD AND APPARATUS FOR DETER- MINING LIQUID LEVEL Donald G. C. Hare, Roslyn, .N. Y., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Original application May 29, 1940, Serial No.

337,864. Divided and this application November 16, 1943, Serial N0. 510,476

8 Claims. (Cl. 250-835) I This invention relates to a method and apparatus for determining the level of a liquid and particularly to the determination of the level of a liquid such as hydrocarbon oil within a conplaced in contact with and moved along the the rays or particles after .these have been scattered and slowed down by'the material through tainer. The principal object of the invention is s which they may pass. This scattering which is to provide a method and apparatus of this type similar to diffuse reflection will cause some of which will indicate accurately the level of a liqthe radiation from the' source to return to the uid within a container without the necessity of detector. The amount of scattering which takes any direct contact with the liquid or of access to place in a given volume of substance, is, for the the inner side of the container wall. 10 more penetrating radiation, some function of the This application is a division 01' my pending density of the scattering material. Thus, when application. Serial No. 337,864, filed May 29, 1940, the level ofthe liquid in the vessel is below the and granted May 16, 1944, No. 2,348,810. region through which the rays from the source It is of course frequently desirable to ascerpass, the detector will indicate little more than, tain accurately the level of a liquid which may 18 the scattered intensity due to the wall of the be contained in a closed vessel. In the past this vessel, since the density of the vapor in the veshas been accomplished by means of gauge glasses sel is low. If, however, the device is placed so or by floats or other similar means. Obviously, that the rays will enter and be scattered b the when the liquid within the container or vessel liquid, there will be a considerable increase in is subjected to conditions of high temperature 20 the scattered intensity indicated by the detector. or pressure or both, or where the liquid possesses due to the fact that the radiation passing a high viscosity, these methods are not entirely through the wall now has a more dense medium, satisfactory. Gauge glasses must be madesuflii. e., the liquid to traverse. v ciently strong to withstand the pressure within For a better understanding or the invention the vessel and these glasses often become reference maybe had to the accompanying drawgummed or clogged so as to render them useless ing in which: or at least inaccurate. Where a float is used, it Figure 1 is a vertical elevation through a conis necessary either to provide some electrical systainer and through an instrument embodying tem whereby contacts are opened and closed by the invention placed substantially at the level the float which, of course, is a dangerous proceof a body of liquid within the container; while dure when the liquid is inflammable, or to pro- Figure 2 is a similar view showing a slightly vide some form of stufling box disposed in the vmodified form of the instrument as used in dewall of the vessel. If the glands of the stufling termining liquid level within a container having box are made suflleiently tight to prevent leakwalls thicker than those shown in Figure 1. age they will usually interfere with the free Referring to the drawing, a closed vessellii movement of the float arm or linkage. is shown as having therein a quantity of liquid In accordance with the present invention, a II, the level of which is indicated at H. The method and apparatus has been provided for dewalls of this container may be of any thickness terminlng the level of the fluid behind the walls up to, say, one inch. of a closed container without the necessity of 40 The liquid level detecting instrument comhaving access to the interior of the container. prises a casing 16 having disposed therein a and without the necessity of any electrical syssource [8 preferably of gamma rays. The source tem inside the container or any moving parts i8 may comprise, for instance, a radium comsueh as a float with its attendant stumng box. pound. Also disposed within the casing 18 is a Further, the wall of the container may be of an device 20 capable of detecting the rays or partidesired material and of considerable thickness. cles which may be scattered within the wall of It should, for instance, be practicable to deterthe container and within the liquid I2 and some mine the liquid level through a wall of steel of of which rays will return so as to contact the from two to four inches or more in thickness. detector. The detector 20 may be connected I In carrying out the invention an instrument electrically to a suitable indicating or recording containing a source of radiation such as gamma instrument 22. The source 18 and the detector rays, neutrons or other penetrative particles 20 are preferably separated b mean of a le d which have the property of being able to pass shield 24 so as to reduce the direct radiation throughthe wall of a container, is adapted to be from the source to the detector. A collimating system comprising shields 26 having slits 2B is provided adjacent the source It so as, to define the area of measurement.

In operation the instrument is placed against the outer sidc'of one vertical wall of the container' Ill, and rays from the source It will pass.

outwardly through the slits 28' into the wall of 'the vessel. A certain amountfof the radiation will be scattered back to the detector 20 by the walls of the vessel, but as long as the walls are fairly uniform or the instrument'is in one position this observed intensity will be fairly constant.v

The. amount of scattering which takes place in a given volume of substance is, for the more penetrating radiation, some'function of the density of the scattering material. Thus, if the instrument is placed above the liquid level It the detector 20 or rather the meter 22 will indicate little more than the scattered intensity due to the wall of the vessel, since the density of the air or vapor in the vessel is substantially negligible. If, however, theinstrument vis placed against the vessel below the liquid level ll, the

- meter 22 will indicate a considerable increase inthe scattered intensity due to the fact that the radiation passing through the wall is scattered not in: the casing l6 vertically-along. the vessel the the meter 22. i I The foregoing discussion refers primarily to the more than one inch in thickness and in this case thegamma rays. from a substance such as radium or thorium may beqused. For vessels 'fw'hose walls are not thicker than this the use of gamma raysis to beipreierred since the techof these rays is somewhat simpler than that for other penetrativeradiation.

nique of measurement 1!, however, it is desired to measure the liquid level in avessel having very thick' walls, another technique maybe employed which will give equally satisfactory results; To this end, in Figure 2 is. shown a vessel v30 having therein a quantity of liquid 82 with the level of the liquid indicated 1 as' at 34. fl'hewalls'of this vessel may be of ."from. sayvone to four inches'in thickness. The

instrument employedin this modification is quite similar to that described in connection with Figure 1 and a casing 38 has disposed therein a source 30' of fast neutrons and a device I capable of detecting slow neutrons, such as an ionisation chamber filled with boron trifiuoride. The

detector 40 is connected to a suitable meter 42 and is separated from the source 38 by means of a lead shield to prevent undesired direct gamma radiation which might otherwise cause an imwanted background effect. The lead will tend .to'preven-t passage of slow neutrons from the source "directly to the detector, and fast neutrons which may pass through the lead are not easily detected by means of the detector ll. In

this case the collimating system 48 having slits I8 is placed adjacent the detector Ill since while fast neutrons will penetrate several inches in even a heavy material, slow neutrons may be easily stopped by such substances ascadmium of which the collimating shields may be formed. The fast neutrons indicated 'by the dotted line- II are little aifected by the walls of the vessel and will pass through a fairly thickpiece of steel without losing much of their, energyor velocity even though they may be widely scattered. However, a fast neutron is very rapidly slowed down in any substance containing hydrogen since the v.25 "onlyby the material of the vessel wall but also i by the liquid within the vessel. Thus,'by mov-' neutron gives up on the average about one half of its energy at each collision with a hydrogen nucleus. These neutrons in the process of being slowed down are also scattered in all directions 5 and many of them will "difluse back through the wall of the vessel to be detected by the device 40. Thus, when a hydrogenic liquid 22 is present in the vessel in the region traversed by the neutrons, a fairly large number of slow neutrons 10 will be detected at 40 and observed at the meter 42, while in the absence of any hydrogenic liquid very few slow neutrons will be observed. Thus, as was the case in connection with the embodiment disclosed in ,Figure 1, it is merely necessary to move the casing 38 vertically along the outside of the vessel 30 and to note the point where the meter 42 will indicate a sudden change in the response of the detector 40.

It is to be understood that this invention can have been described. For instance, if it is desired to maintain a definite liquid level within the container, either of the casings It or 38 may be more or less permanently secured to the outer wall of the vessel at the point at which it is desired to maintain the level of the liquid. Either of the detectors ill .or III can then be connected as. is well known to thoseversed in the art so as to operate suitablecontrol devices such as valves 30 for allowing more or less liquid to pass into the vessel. 'Ei-therof the instruments can also be case where-the walls of the vessel are not much connected so as to operate, a suitable alarm or warning signal.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may

. vessel and returned to a detector near the source,

moving the source and detector, vertically along the vessel wall and noting the point at which a a sudden change in the amount of scattered neutrons is indicated by the detector.

.2. A method of determining the level of a liq- I uid in .a container which comprises placing near the outer surface of the side wall of said container-a source offast neutrons so that the neutrons emitted will pass through said wall and be scattered and slowed down by the material of the wall and by the material within the container, detecting neutrons so scattered and slowed down and returned outwardly through said con- 00 tainer wall, and determining from the number of slow neutrons detected whether or not a liquid is present within the container and opposite the i source of fast neutrons.

3. A method of determining the level of a liquid in a closed container which comprises placing against the outer surface of the side wall of said container a source of fast neutrons so that the neutrons emitted will pass through said wall and be scattered and slowed down by the material 70 within the container, measuring the number of ing thismeasuring operation at a plurality of points displaced vertically along said side wall II and determining from the number of slow neube used in. various other ways than those whichbe made withoutdeparting from the spirit and trons detected at said points the nature of the material present within the container at said points. I

4. A method of determining the level of a liquid in a closed container which comprises placing near the outer surface of the side wall of said container a source of fast neutrons so that the neutrons emitted will pass through said wall and be scattered and slowed down by the material of the wall and by the material within the container, detecting neutrons so scattered and slowed down and returned outwardly through said container wall, and moving the source and detecting means vertically along the outer surface of said wall until a point is reached at which a sudden increase or decrease in the number of return neutrons is indicated by the detecting means.

5. A device for determining the level of a liquid within avessel comprising a housing, said housing being adapted to be placed near the outer surface of a side wall of said vessel, a source of fast neutrons within said housing, a detector of slow neutrons within the housingand an instrument responsive to the output of said detector for indicating the amount of neutrons scattered and slowed down by the material within the vessel and returned outwardly to said detector.

6. A device for determining the level of a liquid in a container, which comprises a housing, a source of fast neutrons in said housing, said housing adapted to be held against the outer surface of the side wall of said container, a device in said housing for detecting neutronsemitted by said source and scattered and slowed down in the material within said container, a shield to reduce direct radiation from said source to said detecting device, a collimating system within said housing and comprising shield members provided with slits for directing a beam of scattered neutrons to the detecting device so as to define the area of measurement, and an instrument connected to said detecting device for indicating the amount of scattered neutrons returned to the detecting device.

7. A device for determining the level of a liquid within a container, comprising a source of fast neutrons, a detector of slow neutrons, means for supporting said source and said detector in a predetermined position near the outer surface of a side wall of said container, means for shielding said detector from direct primary radiation from said source, and an instrument connected to said detector for indicating the amount of neutrons reaching said detector after being scattered and slowed down by the material in the container.

8. A device for determining the level of a liquid within a vessel comprising a housing adapted to be placed near the outer surface of a side wall of said vessel, a source of fast neutrons in said housing, a detector of slow neutrons within the housing, means for shielding said detector from direct primary radiation from such source, means for directing to said detector a beam from neutrons scattered and slowed down within said vessel, and an instrument responsive to the output of said detector for indicating the amount of neutrons in said beam.

DONALD G. C. HARE. 

